GB365710A - Improvements in and relating to the manufacture of cellulose acetate - Google Patents

Abstract

Cellulose acetate is separated from its solutions, for example, ripened acetylation liquors, by a process involving the neutralization of the acidic catalyst by means of a neutralizing agent in substantial excess, and separation of acetic acid by distillation under reduced pressure. By substantial excess of neutralizing agent is meant at least 2 equivalents, for example, about 3 to 5 equivalents when sulphuric acid is the catalyst present, and at least 1,5 equivalents in the case of other acidic catalysts. An alkali salt of acetic acid is the neutralizing agent preferred, but soda ash or caustic alkali may be used. The distillation is preferably carried out at a sufficiently low pressure as to maintain the maximum temperature at about 70 DEG C. The amount of acetic acid recovered by the distillation is at least 40-50 per cent, and if need be, may be over 70 per cent, without injury to the cellulose acetate. Precipitation of the distillation residue may be carried out by incorporating 60-75 per cent of the quantity of water which would be required for the cellulose acetate precipitation to commence, and submerging in customary manner in a bath of precipitating agent. The cellulose acetate may be precipitated in shaped forms of an opaque and uniformly porous character by using the process of Specification 357,552. In an example, (1) to 100 parts of ripened acid dope containing 1,4 parts of sulphuric acid there are added 8 parts of anhydrous sodium acetate, and the resulting solution is subjected to a slow distillation under reduced pressure until 35 per cent of the acetic acid present has been recovered; 15 parts of water are incorporated with the residue which is then ribboned between rollers or belts surfaced with absorbent material, as in the process of Specification 357,552, and precipitated in water. According to further examples, a ripened acid dope, as in example (1), is neutralized by the addition of 3,5 equivalents of sodium acetate and (2) distilled until 45 per cent of the acetic acid has been recovered after which 13 parts of water are added, or (3) distilled until 60 per cent of the acetic acid has been recovered, when 10 parts of water are added. The precipitation in each case then proceeds as in the first example.